The present invention relates to a method of triggering restraint means in a motor vehicle in the event of an impact and/or a collision with an object. The method primarily relates to the triggering of non-reversible restraint means, such as pyrotechnic seatbelt tighteners and airbags. For this purpose, the time characteristic of the acceleration is detected in the form of at least one acceleration signal. The time characteristic of a velocity is then generated from the acceleration signal. A threshold value for the velocity is determined as a triggering criterion.
Conventionally, airbag control devices measure the acceleration in the passenger compartment in the event of an accident and, on the basis of this acceleration, determine when restraint means, such as seatbelt tighteners and airbags, must be triggered.
A method of triggering restraint means in a safety system for vehicle occupants is discussed in European Patent No. 0 458 796, in which an acceleration signal is detected with the aid of a suitable acceleration sensor. Through integration over time, possibly in combination with suitable weighting, this acceleration signal is converted into a velocity. A threshold value is used as a triggering criterion for the velocity. In the method of European Patent No. 0 458 796, the threshold value is determined as a function of one or more state variables or of prior state variables of the motor vehicle. For example, the acceleration signal itself, a signal derived therefrom, such as the velocity, or even the time passing during the crash may be considered as state variables.
The threshold value is selected in the context of the conventional method in such a manner that it ensures safe and reliable triggering of the necessary restraint means in all impact situations coming into consideration, independent of the type of collision partner and the impact velocity, i.e., the relative velocity between the motor vehicle and the collision partner. Dynamic adaptation of the threshold value to the specific impact situation is not possible here, since in this case, neither a suitable sensor system nor a corresponding signal analysis system is provided.
In accordance with an exemplary embodiment of the present invention, a method is provided in which the triggering of restraint means, such as airbags and seatbelt tighteners, is better adapted to the specific impact situation and unnecessary triggering of restraint means may be avoided.
This may be achieved according to an exemplary embodiment of the present invention in that the impact velocity and the instant of impact are established with the aid of a pre-crash sensor system before the impact. The impact situation is classified with reference to the impact velocity. A triggering time window, in which the time characteristic of the velocity is generated, is determined with the aid of the classification of the impact situation, and, in parallel to this, a threshold value for the velocity is established from the acceleration signal, the classification of the impact situation being taken into consideration.
According to an exemplary embodiment of the present invention, the conventional xe2x80x9csingle point sensing systemsxe2x80x9d may be expediently expandable by a pre-crash sensor system to be installed in the motor vehicle in order to detect possible collision partners in the surroundings of the vehicle beforehand. With the aid of the pre-crash sensor system, the impact velocity (closing velocity vclose) and the instant of impact (t0), i.e., the time difference until the impact against the object, may be established. If the pre-crash sensor system includes at least two pre-crash sensors arranged in a suitable manner, the offset, i.e., the impact point and the impact angle, may additionally be determined using a triangulation method. In the context of the pre-crash sensing, radar measurements, infrared measurements, or even optical measurement methods may be used.
Furthermore, according to an exemplary embodiment of the present invention, the impact situations in consideration may expediently be classified with reference to the impact velocity, since the impact velocity alone may provide information about the severity of the crash. The optimum triggering time and the maximum necessary restraint means may be a function of further parameters, such as the type of impact, the mass ratio of the collision partners, and the ratio of the rigidities of the collision partners. Furthermore, the classification of the impact situation on the basis of the impact velocity according to an exemplary embodiment of the present invention may allow the localization to a triggering time window [tA . . . tB] of the triggering time which is to be established. This may provide the possibility of including information about the course of the crash after instant of impact t0 until beginning tA of triggering time window [tA . . . tB] in the determination of the threshold value. In addition, the generation of the time characteristic of the velocity from the acceleration signal may now be restricted to the triggering time window.
Additionally, according to an exemplary embodiment of the present invention, it may be expedient to consider the specific impact situation while determining the threshold value from the acceleration signal, since, for example, higher impact velocities may require more sensitive triggering of the restraint means than lower impact velocities. Therefore, according to an exemplary embodiment of the present invention, the classification of the impact situation is also considered while establishing the threshold value.
In an exemplary method according to the present invention, the maximum necessary restraint means in an impact situation are also determined with the aid of the classification of the specific impact situation.
There are various possibilities for classifying the impact situations with reference to the impact velocity. In a variant for two-stage restraint means, velocity clusters in the form of velocity ranges for the impact velocity are formed, the cluster limits being selected according to the respective maximum necessary restraint means. In this case, the velocity clusters are defined as the velocity ranges in which, for all impact situations in consideration,
either no restraint means are necessary (cluster C0)
or the first stage of the restraint means is necessary in the belted state for some of the impact situations in consideration, while restraint means are not yet necessary in the belted state (cluster C1),
or the first stage of the restraint means is necessary in the belted state for some of the impact situations in consideration, while the second stage of the restraint means is not necessary in the unbelted state or in the belted state (cluster C2),
or the first and second stages of the restraint means are necessary in the unbelted state for some of the impact situations in consideration, while the second stage of the restraint means is not necessary in the belted state (cluster C3),
or the first and second stages of the restraint means are necessary both in the unbelted state and in the belted state for some of the impact situations in consideration (cluster C4).
In the context of the classification of a specific impact situation, the corresponding impact velocity is assigned to one of these velocity clusters. The maximum necessary restraint means may then be determined easily on the basis of the classification of the impact situation and/or the assignment to the corresponding velocity cluster.
The above-described classification of the impact situations may be advantageous because the triggering time window for a specific impact situation may be established easily with the aid of the velocity values which form the cluster limits of the velocity cluster assigned to the corresponding impact velocity.
In the context of an exemplary method according to the present invention, the time characteristic of a velocity is generated from the acceleration signal. There are also various possibilities in principle for this purpose. In an exemplary embodiment, the acceleration signal is integrated over time. The working signal resulting from this may then also be weighted using a suitable weighting function. However, the acceleration signal may also be weighted first in order to subsequently integrate the working signal resulting therefrom over time. It may also be possible to perform two weightings, namely a first weighting before the integration over time and a second weighting after the integration over time.
As mentioned above, according to an exemplary embodiment of the present invention, the classification of the impact situation is also taken into consideration in establishing the threshold value. In an exemplary method according to the present invention, the acceleration signal is filtered and/or transformed to establish the threshold value, the transformation being able to be performed before or after the filtering. In this case, it may be advantageous if at least some of the filter parameters and/or the transformation parameters are determined as a function of the respective classification of the impact situation, in order to take the specific impact situation into consideration.
In an exemplary method according to the present invention, the object, i.e., the collision partner, is classified with regard to its mass and its rigidity by analyzing the time characteristic of the acceleration after the instant of impact. This object classification may then also be taken into consideration in determining the threshold value, which additionally contributes to a more precise determination of the triggering time and the maximum necessary restraint means.
For object classification, on the one hand, the interaction of the motor vehicle with the object at the beginning of the impact may be analyzed as a function of the classification of the impact situation. In this connection, it may be advantageous to perform and analyze a short-time integration of the acceleration signal after the instant of impact in order to detect strong signal peaks at the beginning of the impact, and/or to analyze the signal rise after the instant of impact.
On the other hand, for object classification, fracture occurrences in the motor vehicle and changes in the barrier hardness in the course of the impact may be detected via high-frequency oscillations in the acceleration signal and analyzed as a function of the classification of the impact situation. The high-frequency oscillations in the acceleration signal may be detected easily with the aid of a high pass filter. The analysis may then be performed via peak values.
In an exemplary method according to the present invention, the acceleration signal is additionally analyzed even before the actual impact up to the instant of impact in order to recognize any pre-displacement of the vehicle occupants and/or an xe2x80x9cout of positionxe2x80x9d situation before the impact and to take this into consideration when triggering the restraint means. Corresponding information may be obtained by integrating the acceleration signal twice and combined with further occupant parameters, such as the seat position, the steering wheel setting, and/or the occupant weight.